It is known that pressure variations or pulses may occur when fluids are pumped through conduits. These pressure variations and the resulting mechanical vibrations can disrupt the constant flow of the fluid and cause damage and wear to the pipes and connections. Moreover, such pressure variations can disrupt or ruin downstream applications, which may depend on smooth, steady flow for their proper function. To address these problems, pulse dampeners have been developed to reduce or eliminate pulsations and vibrations in the fluids as they are pumped through pressurized systems.
Applications for pulse dampeners include, for example, liquid chromatography, where pulses in fluid flow can obscure chromatographic analysis, as well as in other applications such as other analytical instrument systems, including flow cytometry, urinalysis and hematology analyzers, chemical analysis systems, flow cells used in molecular analysis, and other applications in which concentration is measured as a function of time.
Conventional pulse dampening systems exist, and take a variety of forms. One such method uses air and air pressure to try to counteract and compensate for the pressure exerted by a pressurized fluid moving through the dampener. Conventional pulse dampeners or surge suppressors that do not use elastic membranes have incorporated air chambers such that the fluid being pumped through the conduit is allowed to compress the air in the air chamber and occupy a greater proportion of the volume of the chamber as the fluid pressure increases. When the fluid pressure decreases, the air in the chamber expands and returns some of the fluid from the chamber to the conduit system. A problem with the above approach using one or more air chambers that communicate with the fluid channel, however, is that some of the air will likely dissolve into the fluid being pumped, thereby reducing the volume of air in the chamber and potentially affecting the composition of the fluid being pumped.
An alternative approach that reduces this problem is to use a dampening membrane which separates the fluid being pumped through the conduit system from an air chamber used to compensate for the fluid pressure. In such systems, the fluid exerts pressure on the membrane, causing it to expand toward the air pressure chamber, and the air in the chamber pushes back on the membrane to compensate for that pressure and membrane displacement. Conventional pulse dampeners that use this method may use a closed air chamber with a static amount of air. However, experience teaches that just about every membrane is at least somewhat gas-permeable—particularly when the membrane is thin, as is often desired to achieve good dampening performance. Thus, this approach often results in the loss of air from the air chamber, and the undesirable gasification of the liquid being pumped.
An alternative to using an air-filled chamber to provide the restoring force on the liquid, is to use alternative means, such as a compressible liquid, a spring, or a thick, but squishy piece of rubber or foam. An example of such a device is that disclosed in U.S. Pat. No. 4,629,562, titled “Pulse Dampener” and issued to Kercher on Dec. 16, 1986. The Kercher patent explains that a pulse dampener may be used in a liquid chromatography system and teaches the use of a chemically inert diaphragm and a unitized plug which has two portions, each of which has different compressibility characteristics. However, in such a device, gasses may still find their way into the liquid through leaks in the system, by incomplete priming of the device, or by introduction of air bubbles into the fluid flow itself. Once introduced into such a dampener, such air-bubbles can be extremely hard to remove, and they influence the performance of the dampener in unpredictable ways.
Another example can be found in U.S. Pat. No. 4,548,240, titled “Hydraulic Pulse Dampener and Employing Stiff Diaphragm and Nesting Member,” and issued to Graham on Oct. 22, 1985. Graham teaches an example of a hydraulic pulse dampener which uses liquid to dampen pulses in a relatively high-pressure environment. However, Graham does not provide for any degassing capability. Likewise, U.S. Pat. No. 4,222,414, titled “Pulse Dampener for High Pressure Liquid Chromatography,” and issued to Achener on Sep. 16, 1980, and U.S. Pat. No. 4,234,427, titled “Pulse Dampener,” and issued to Boehme on Nov. 18, 1980, both disclose hydraulic pulse dampeners for use in relatively high-pressure environments, but the apparatus disclosed in both Achener and Graham lack any degassing or de-bubbling capabilities.
Air bubbles trapped in a dampener can result in several undesirable consequences. First, the presence of bubbles can affect the dampening power of the pulse dampener. The dampening power of the pulse dampener can vary in direct proportion to the varying size of the bubbles generated by or introduced into the system, and therefore the system may not uniformly dampen fluid pulses. In such situations, the dampening ability may be variable and unpredictable. Second, bubbles may unintentionally exit the pulse dampening system and travel downstream in the system. In some applications, such as liquid chromatography, the presence of bubbles in the fluid stream is undesirable. Third, gas bubbles trapped in a fluid pulse dampening system may cause gas buildups within the system, thereby reducing the ability to cleanly and fully sweep a fluid through the system.
The problem of dissolved gas or bubbles within pulse dampening systems has met with some efforts at resolution, but these results and approaches have several drawbacks and limitations. For example, U.S. Pat. No. 5,904,181, titled “Pulse Dampening Device,” and issued to Tooma et al. on May 18, 1999, discloses a pulsation dampening device with a horizontal shape and with fluid inlet and outlet ports configured so as to minimize air bubbles from becoming trapped within a fluid. However, Tooma et al. fails to disclose or provide a system for extracting air bubbles that do become trapped.
Similarly, U.S. Pat. No. 6,675,835, titled “Elliptical Tubing in Degassing and Pulsation Damper Application,” issued to Gerner et al. on Jan. 13, 2004 discloses a flow-dampening and degassing apparatus which uses a gas-permeable, non-porous, elliptical-shaped tube disposed within a vacuum chamber. Besides the cost and complexity of requiring a vacuum chamber, Gerner et al. has the further limitation of having a membrane which must perform both the dampening and degassing functions. Thus, the functions of the two membranes cannot be separately optimized to account for different types of fluid by, for example, the use of different materials, shapes, or sizes for the membranes.
Likewise, U.S. published patent application No. 2003/0041911, titled “Burdoin (sic) Tubing in Degassing and Pulse Dampener Applications,” filed on behalf of Gerner et al., discusses integrating a degasser function and a dampening function, but do so using a Bourdon tube as the dampening element and thus require a more complex dampening system. In addition, because the degassing tube and the dampening tube in the Gerner et al. patent application are one-and-the-same, one cannot independently optimize the dampening characteristics and the degassing characteristics.
The foregoing U.S. Pat. Nos. 4,548,240, 4,222,414, 4,234,427, 5,904,181, and 6,675,835, and U.S. published patent application No. 2003/0041911, are hereby incorporated by reference as if fully set forth herein.
The use of both a conventional pulse dampener and a conventional degasser or de-bubbler in a given system remains a possibility, but also involves limitations and drawbacks. For example, such an approach involves the use of two separate components in a system, thus making the system more complex, and introducing more internal volume into the system. Moreover, this approach involves the use of more fluid connections (and thus more work for an operator and greater chance for leaks) and also additional costs due to the use of two components.